Nanocomposite Metal Oxides: An Easy Way to Design Catalysts with Desired Functional Properties

Nanosized composite materials are getting more and more important because or their characteristics and properties. In particular an accurate choice of the supporting and the supported materials can allow obtaining systems characterized by specific and tunable behaviour. Thanks to their versatility this is particularly true for oxide based nanocomposites. In this contribution several oxide based nanocomposites have been prepared by wet impregnation and characterized by means of X-Ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transform (DRIFT) Spectroscopy, X-Ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) and Transmission Electron Microscopy (TEM). The supporting oxides (cobalt oxide, ceria, yttria stabilized zirconia, YSZ…) have been selected taking into consideration the technological aspects, the reactivity, the possibility to prepare them by easy, reproducible, environmentally and economically sustainable methods. Similar consideration guided the choice of the supported oxide (nickel oxide, iron oxide, cobalt oxide, tungsten oxide, cerium oxide, …). Firstly, the growing mode was investigated. In general different growing methods can been hypothesized: from layer by layer (Frank-van der Merwe), to 3D island growing (Volmer-Weber). The obtained results suggest a significant influence of the composition on the growing method. XPS allowed to study the interface between supported and supporting oxide indicating a chemical interaction that can originate intermediate oxidation states. The metal oxide deposition may modify the active (acidic/basic and redox) sites type and distribution as determined by means of the chemisorption of probe molecules (pyridine, carbon monoxide, carbon dioxide) followed by DRIFT spectroscopy. The interaction with methanol has also been investigated and the obtained results have been discussed taking into consideration the active site distribution. Methanol is an important probe molecule being an intermediate in several oxidation reactions; moreover, methanol can also be a promising fuel for fuel cells. Methanol can interact with the sample surfaces molecularly or dissociatively (giving rise to methoxy groups) depending on the composition, preparation procedure, thermal treatments … The reactivity with respect to methanol changes with the investigated system and composition. Activity also differs for the different systems: different reaction temperature and selectivity can be obtained by choosing, as an example, appropriate compositions.